This application claims the priority of Korean Patent Application No. 2003-92590, filed on Dec. 17, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a method for supporting a multicast service, and more particularly, to a method for supporting a multicast service in an Ethernet Passive Optical Network (EPON).
2. Description of the Related Art
To allow an EPON system to support a multicast service, an Optical Line Terminal (OLT) system must support a multicast service for each port of each line card, and a PON (Passive Optical Network) port of the OLT system must support a multicast service for each Optical Network Unit (ONU) system. Also, the ONU system must support a multicast service for each subscriber port.
An OLT system supports a multicast service for its ports using L3 (Layer 3) routing and multicasting, while an ONU system supports a multicast service according to an IGMP (Internet Group Management Protocol) snooping method that processes L3 multicast packets using a L2 (Layer 2) switch. In this case, since the OLT system handles a PON port to which a plurality of ONU systems are connected, when the OLT system performs a L3 multicast service, multicast packets that should be sent to specific ONU systems are transmitted to all ONU systems connected to the PON port. As a result, an ONU system whose multicast address exists in a L2 multicast forwarding table can send a multicast packet to a subscriber port belonging to a corresponding multicast group, however, the other ONU systems whose their multicast addresses don't exist in the L2 multicast forwarding table flood the multicast packet. Accordingly, a problem is generated that all subscribers belonging to the ONU system receive the multicast packet having no concern with them.